It may seem inappropriate to investigate chloroplast DNA (cpDNA) or  mitochondrial DNA (mtDNA) to get insights of gene flow in plants. Indeed, the bulk of gene exchanges is mediated by pollen, and cytoplasmic genomes are usually maternally inherited. But seed flow may be significant in some species, whereas cpDNA is paternally inherited in an important group of  forest trees (Gymnosperms). In general, inferring the relative importance of  pollen and seed flow seems important. Indeed, even if often less mobile than pollen grains, seeds are the only vehicle to move to new environments ('The haploid phase of environmental exploration cannot act further than what has  already been colonized by the diploid phase' to quote Harper). Also, for some species, humans have moved seeds and plants around. Cytoplasmic markers may in such cases be extremely useful to differentiate introduced from native material. Indeed, genetic structure is often much stronger for maternally inherited markers compared to biparentally (or paternally) inherited ones.  In parentage analyses, a set of highly polymorphic nuclear microsatellites may be used to identify the parents of a given seedlings but the differentiation  of the mother from the father may be difficult. On the other hand, if combined with cytoplasmic markers, a complete picture may be obtained.  Clonally evolving genomes are very appropriate for reconstructing phylogenies, an information sometimes useful to consider in gene flow studies. Finally, 'interspecific gene flow' also called 'cytoplasmic  captures' are reported to be very frequent in plants.  Actually, these  expressions may be misleading, since it is probably often the nuclear genome which moves over a static maternal bedrock. Nevertheless, it remains true that one may often get better insights of interspecific gene flow with  cytoplasmic than with nuclear markers.